The mammalian dentition is a complex organ whose normal development is of major health importance, yet whose dysgenesis and deterioration have been grossly under-studied. The dentition is also an important model system for the genetics of complex, segmented organs that develop through tissue interactions. This research-initiation project will investigate regulatory gene expression patterns in mouse tooth germs. First, mRNA obtained from 10. 5 daytooth germs will be screened by polymerase chain reaction (PCR) methods to amplify all expressed homeotic (Hox) genes. The amplified products will be sequenced and identified; previously unidentified genes will be cloned and mapped using a mouse genome library. Similar procedures will be used for Int-2, Collagen I, and tenascin (and closely homologous genes), that are involved in the control of cell differentiation and extra-cellular matrix production. In situ hybridization will be done on sections of tooth germs at various developmental ages and in morphologically distinct parts of each tooth, to develop a spatio-temporal regulatory expression map for genes identified as above. Finally, work will be done to develop PCR-based methods for improved sensitivity in microhistological expression analysis. This study will lay the ground work for systematic investigations of cell-cell interaction, neural crest function, and the morphogenetics of mammalian teeth, with direct application to the human dentition and to dental dysgenesis. This is responsive to NIDR's Small Grants Program, as a research retraining initiative for Kenneth M. Weiss, and an extension of ongoing methods to a new area for Frank H. Ruddle.